The well-known advantages of a polymer having chains containing directly linked polycyclic repeating units free of unsaturation, have driven those skilled in the art to search for a processable `addition polymer` of one or more multi-ringed monoolefinically unsaturated cycloolefin monomers such as norbornene, bicyclo[2.2.1.]hept-2-ene or "NB" for brevity, and substituted embodiments thereof, such as ethylidenenorbornene or decylnorbornene, and particularly those monomers of NB having at least one substituent in the 5- (or 6-) positions. The foregoing monomers are collectively referred to herein as "norbornene-type" or "NB-type" monomers, for convenience, recognizing that, just as in NB, or substituted NB, each NB-type polymer is characterized by containing a repeating unit resulting from an addition polymerized derivative of bicyclo[2.2.1.]-hept-2-ene. A first NB-type or NB monomer may be polymerized by coordination polymerization to form (i) an addition homopolymer; or, (ii) with a second NB-type or NB monomer, either one (first or second) of which is present in a major molar proportion relative to the other, to form an addition NB-type copolymer; or, (iii) with a second monomer which is not an NB-type monomer, present in a minor molar proportion relative to the first, to form an addition copolymer with plural repeating units of at least one NB-type monomer.
Besides NB and substituted NB, a monomer with a NB-type configuration may be a multi-ringed cycloolefin having up to four fused rings, in which one or more of the rings may have an acyclic (C.sub.1 -C.sub.20)alkyl, (C.sub.1 -C.sub.20)haloalkyl, (C.sub.3 -C.sub.20)alkenyl, or (C.sub.1 -C.sub.6)alkylidene substituent. Each chain of the addition polymer formed herein is characterized by having at least one non-styrenic terminal double bond. The addition polymer, substantially 2,3-enchained (based on Chemical Abstracts Service numbering), may be a homopolymer of a NB-type monomer; or, a copolymer of two or more NB-type monomers, e.g. NB and 5-dodecylNB; or, a copolymer of a NB-type cyclomonoolefin with a NB-type cyclodiolefin, e.g. NB or 5-hexylNB and dicyclopentadiene (DCPD); or, a copolymer of a NB-type monomer with a cyclomonoolefin e.g. NB or 5-decylNB and cyclopentene, cyclohexene or cyclooctene; or, a copolymer of a NB-type cyclomonoolefin with a non-NB type cyclodiolefin, e.g. NB or 5-decylNB and cycloheptadiene or cyclooctadiene.
Polynorbornene or "poly(bicyclo[2.2.1.]-hept-2-ene)" or polyNB for brevity, was originally produced a long time ago (U.S. Pat. No. 2,721,189). However this original material was found to contain two types of polymers, one brittle, the other thermoformable and `drawable`. The brittle polymer was later found to be a low molecular weight (`mol wt`) saturated polymer which was termed an addition type polymer; and, the thermoformable polymer was shown to be formed by ring opening metathesis polymerization (`ROMP`). A ROMP polymer has a different structure compared with that of the addition polymer in that (i) the ROMP polymer of one or more NB-type monomers, contains a repeat unit with one less cyclic unit than did the starting monomer, and, (ii) these are linked together in an unsaturated backbone characteristic of a ROMP polymer and is shown below. ##STR1##
It will now be evident that, despite being formed from the same monomer, an addition-polymerized polyNB is clearly distinguishable over a ROMP polymer. Because of the different (addition) mechanism, the repeating unit of the former has no backbone C.dbd.C unsaturation while that of a ROMP always does.
The difference in structures of ROMP and addition polymers of NB-type monomers is evidenced in their properties, e.g. thermal properties. The addition type polymer of NB has a high T.sub.g of about 370.degree. C. The unsaturated ROMP polymer of NB exhibits a T.sub.g of about 35.degree. C., and exhibits poor thermal stability at high temperature above 200.degree. C. because of its high degree of C.dbd.C unsaturation.
Some time later, reaction conditions were optimized so as to enable one to choose, and selectively make, either the low mol wt addition polymer, or the ROMP polymer. In U.S. Pat. No. 3,330,815, the disclosure taught that only the addition polymer was synthesized with TiCl.sub.4 /Et.sub.2 AlCl or Pd(C.sub.6 H.sub.5 CN).sub.2 Cl.sub.2, under particular conditions, except that the polymers produced were only those in the mol wt range from 500 to 750 in which range they were too brittle for any practical application.
Very recently, the addition polymer of norbornene was found to have been produced in two forms. The first form is an amorphous polymer which shows a glass transition temperature of about 370.degree. C. It is this amorphous addition polymer of one or more NB-type monomers which is the subject of this invention. The second form was found to be a highly crystalline form of a "norbornene-addition polymer", that is, an addition polymer of a NB-type monomer, which polymer is totally insoluble in halohydrocarbons and aromatic solvents, and reportedly does not melt until it decomposes at .apprxeq.600.degree. C. (under vacuum to avoid oxidation). It is therefore unprocessable. (W. Kaminsky et al., J. Mol. Cat. 74, (1992), 109; W. Kaminsky et. al. Makromol. Chem, Macromol. Symp., 47, (1991) 83; and W. Kaminsky, Shokubai, 33, (1991) 536.). This second form has only been shown to be produced with "zirconocene type" catalysts such as those taught by Kaminsky et al, and others, all well known to those skilled in the art. An added distinguishing characteristic of the zirconocene catalyst system is that it catalyzes the copolymerization of ethylene and norbornene. In such copolymers, the amount of NB incorporated into the ethylene/NB copolymer can be varied from high to low (W. Kaminsky et. al. Stud. Surf. Sci. Catal. 56, (1990), 425).
The catalyst of our invention does not incorporate ethylene into the polymer formed, except one mole per chain, at only one terminal end thereof. As will presently be evident, the term "catalyst" is used because the function of the organometal complex is that of both an initiator of a chain as well as that of its termination by inciting .beta.-hydride elimination. Moreover, the term "catalyst" is routinely used in the art to describe complexes such as this, recognizing what the function of the organometal complex in the polymerization reaction actually is. The polymer formed with a zirconocene catalyst can incorporate ethylene in its backbone, randomly, whether in runs of a multiplicity of repeating units, or even a single unit. It should also be noted that the ionic metallocene catalysts, such as zirconocene and hafnocene in combination with the same or different cyclopentadienyl rings use metals from Group IVB as the cation with a compatible weakly coordinating anion. These catalysts are entirely distinct from the catalysts used in this invention.
The phrase "compatible weakly coordinating anion" refers to an anion which is only weakly coordinated to the cation, thereby remaining sufficiently labile to be displaced by a neutral Lewis base. More specifically the phrase refers to an anion which when functioning as a stabilizing anion in the catalyst system of this invention does not transfer an anionic substituent or fragment thereof to the cation, thereby forming a neutral product. Compatible anions are anions which are not degraded to neutrality when the initially formed complex decomposes.
The preformed, single-component Ni-complex catalyst used in this invention, in combination with a predetermined amount of an olefin with a terminal double bond, functions as an efficient chain transfer agent (CTA), and reliably produces melt-processable higher mol wt polymers of predetermined weight average molecular weight M.sub.w in the range from about 1,000 to about 2,000,000 or more. By "olefin with a terminal double bond" we refer to an olefin which has a CH.sub.2 .dbd.CH--R' structure, wherein R' represents hydrogen or a hydrocarbyl group.
The M.sub.w range given above is determined relative to polystyrene by GPC (gel permeation chromatography). The absolute M.sub.w as determined by GPC/Low Angle Light Scattering in cyclohexane at room temperature (22.degree. C.) with a smoothed Light Scattering calibration curve, is about 1.5 times higher in the mol wt range from about 18,000 to 10.sup.6. Above this range, because of "exclusion", the ratio 1.5 is less reliable.
A NB-type polymer with a M.sub.w which is controllable within a desired relatively narrow range, is produced by using a hydrocarbon with a single olefinic double bond, most preferably an .alpha.-olefin, as a CTA in a minor amount relative to the cycloolefins being polymerized, and proportioned to provide the desired mol wt, the more olefin used, the lower the mol wt of the copolymer. The resulting cycloolefin (co)polymer has a characteristic terminal double bond which results from a .beta.-hydride elimination reaction terminating a propagating chain. Such chain transfer is of the type described in typical Ziegler-Natta olefin polymerization and results in each chain formed having an olefinic termination, the double bond being nearest the last cyclic repeating unit. See Polypropylene and other Polyolefins Polymerization and Characterization by Ser van der Ven, Studies in Polymer Science 7, Elsevier Amsterdam, etc. 1990, Chapter 1 POLYPROPYLENE; CATALYSTS AND POLYMERIZATION ASPECTS by Brian L. Goodall, and Section 1.6 thereof titled "The Effect of Catalyst and Process Variables on the Molecular Weight and its Distribution ("Chain Transfer"), and particularly Section 1.6.3 On The Mechanism of Chain Transfer, pg 82-83].
An attempt to copolymerize a C.sub.4 -C.sub.12 olefin with a typical monoolefinically unsaturated monomer such as styrene in a Ziegler-Natta polymerization is unsuccessful because the double bond is essentially unavailable, and the olefin cannot function as a CTA. However, when the olefin is ethylene in the polymerization of a NB-type monomer, the ethylene ends up as vinyl end group. If the chain of addition-polymerized cycloolefin repeating units is not too long, the vinyl end group affords a polymerizable macromonomer or oligomer having from about 4 to 50, preferably from 4 to 20 NB-type repeating units (referred to as a "20-mer"). The mechanism by which an .alpha.-olefin affects both, initiation and propagation rate, in a different polymerization system, namely, the cobalt-catalyzed polymerization of butadiene (to butadiene rubber) was known, as stated by Goodall supra, at pg 83, but the rate at which the reaction occurs, and the amount of butadiene which is incorporated in the rubber chains is not predictable, necessitating the presence in the reactor, of a major molar amount of .alpha.-olefin relative to the butadiene. From the foregoing considerations there is no basis in the art to predict the effect of an .alpha.-olefin on the polymerization of a NB-type monomer.
Thus, to make a polyNB macromonomer having a M.sub.w in the range from 500 to 3,000 (corresponding to from 4 to about 20 linked repeating units), one simply uses the calculated molar amount of olefin, based on the desired chain length, for the CTA. In an analogous manner, a melt-processable polymer in the range from 20,000 to 500,000, more preferably, from 50,000 to 500,000, is made by using a proportioned amount of olefin, and if desired, even higher mol wts which are not melt-processable. The ease with which either a macromonomer, or a melt-processable (co)polymer is made, is a function of the characteristics of the particular cycloolefin species being (co)polymerized.
Research has continued toward the production of a melt-processable addition polymer of a NB-type monomer, and is the subject of an on-going effort. By "melt-processable" it is meant that the polymer is adequately flowable to be thermoformed in a temperature window above its T.sub.g but below its decomposition temperature. To date, there has been no disclosure of how to solve the many problems inherent in the production of a heat-resistant, yet thermoformable and processable polymer of a NB-type monomer which polymer can be extruded, injection molded, blow molded, and the like, using conventional equipment. This invention provides such polymers. For obvious reasons, crystalline NB polymers which do not melt and are insoluble in conventionally used solvents are unsuitable for such "forming" or "drawing" operations.
To date, we know of no practical or reliable method for commercially producing an amorphous NB-addition polymer with controlled mol wt. Polymers formed with too low a mol wt are too brittle to be thermoformed. Polymers with too high a mol wt can only be cast from solution and are not thermoformable. The goal has been to produce an addition polymer having a mol wt M.sub.w in the range of 50,000 to 500,000, using only one or more NB-type monomers, in a reliably controlled manner. The only method available to produce such a polymer has been through premature deactivation of the catalyst systems which produce amorphous polymers of NB, the homopolymers having mol wts in the millions. Predictably, this method of mol wt control leads to low catalyst productivity and requires the use of high catalyst levels when the mol wt M.sub.w is in the range from about 150,000-350,000. Since the problem of forming a processable NB-type polymer was never solved, the second, equally serious problem of obtaining a useful or practical level of conversion was never addressed.
A few years ago the reactivity of cationic, weakly ligated, transition metal compounds was studied in the polymerization of olefins and strained ring compounds, (A. Sen, T. Lai and R. Thomas, J. of Organometal. Chemistry 358 (1988) 567-568, C. Mehler and W. Risse, Makromol. Chem., Rapid Commun. 12, 255-259 (1991)). Pd complexes incorporating the weakly ligating CH.sub.3 CN (acetonitrile) ligand in combination with a weakly coordinating counteranion could only be used with aggressive solvents such as acetonitrile or nitromethane. When Sen et al used the complexes to polymerize NB, a high yield of a homopolymer which was insoluble in CHCl.sub.3, CH.sub.2 Cl.sub.2 and C.sub.6 H.sub.6, was obtained.
The identical experimental procedure, with the same catalyst and reactants, when practiced by Risse et al used one-half the molar amount of each component. Risse et al reported the synthesis of a polyNB homopolymer which had a mol wt M.sub.n of 24,000. In other runs, using different ratios of NB to Pd.sup.2+ -compound, polyNBs having mol wts M.sub.n of 38,000 and 70,000 respectively with narrow dispersities M.sub.w /M.sub.n in the range from 1.36 to 1.45, and viscosities in the range from 0.22 to 0.45 were made. A homopolymer which had a viscosity of 1.1 was synthesized, which upon extrapolation from the mol wt data given for the prior runs, indicates the M.sub.w was over 10.sup.6. See Mehler and Risse Makromol. Chem., Rapid Commun. 12, 255-9 (1991), experimental section at the bottom of page 258 and the GPC data in Table 1 on pg 256. The polymers were soluble in 1,2-dichlorobenzene in which Risse el. al. measured mol wts by GPC (gel permeation chromatography) and viscosimetry, as did Maezawa et al in EP 445,755A, discussed below.
Maezawa et al disclosed the production of high mol wt NB polymers with a two-component catalyst system. The disclosure states that the polymer is preferably formed in the range from 10.sup.5 to 10.sup.7. The manner of obtaining the desired mol wt is shown to be by terminating the polymerization reaction after a predetermined period. Such termination is effected by decomposing the catalyst with an external terminating agent such as acidified methanol, which is added to the reaction to stop the polymerization. There is no internal control of the mol wt within a predetermined range by an agent that does not deactivate the catalyst.
Specifically, three known methods of controlling the mol wt are suggested: (i) varying the amount of the transition metal compound used; (ii) varying the polymerization temperature; and (iii) using hydrogen as a chain transfer agent "CTA" (see page 9, lines 20-23 of the '755A reference) as suggested by Schnecko, Caspary and Degler in "Copolymers of Ethylene with Bicyclic Dienes" Die Angewandte Makromolekulare Chemie, 20 (1971) 141-152 (Nr.283). Despite the foregoing suggestions, there is no indication in '755A that any of them was effective, as is readily concluded from the illustrative examples in the specification. As stated in their illustrative Example 1 in which the catalyst included a combination of nickel bisacetylacetonate (`Ni-acac.sub.2 `) and methaluminoxane ("MAO"), a polyNB having M.sub.w =2.22.times.10.sup.6 (by GPC) was formed. As shown in Table 1 of the '755A reference, only Exs. 5, 6 and 7, in which the (triphenylphosphine)Ni-containing catalysts were used, made homopolymers with M.sub.w =234,000; 646,000; and 577,000 respectively. These nickel catalysts with a triphenylphosphine ligand, are shown to have relatively lower productivity than the biscyclooctadienylnickel (Ex 3) and biscyclopentadienylnickel (Ex 4) which were also used.
One is therefore led to conclude that only those Ni-based catalysts which have substantially lower productivity than Ni(acac).sub.2 with a MAO catalyst system would effectively decrease the mol wt of the homopolymer produced. There is no suggestion that any of the polymers disclosed in the '755A reference are likely to be melt-processable. A conclusion that they are not melt-processable is supported by the evidence that all the polymers made by Maezawa et al were cast from solution.
A key aspect of the '775A disclosure was that the catalyst system disclosed was a combination of at least two components, namely, a transition metal complex catalyst, and a methaluminoxane co-catalyst. Maezawa et al used this multicomponent catalyst system to produce the high mol wt polymers in the range above 5.times.10.sup.5. It was critical that the transition metal component in the complex be from Groups VB, VIB, VIIB, and VIII, and that it be paired with the methaluminoxane co-catalyst in order to produce polymer in a reasonable yield. The criticality of the co-catalyst was confirmed by illustrative examples of transition metal compounds which were generally catalytically effective only so long as methaluminoxane was the co-catalyst (Comparative Examples 3, and 4). The experimental evidence indicated that attaining a high productivity catalyst system was limited to specific nickel complexes in combination with MAO as the activator. All the illustrative examples having been run in toluene, it is evident that they were unaware that a polar solvent such as a halocarbon, acetonitrile, propylene carbonate, and the like, might improve productivity.
It is evident that the results obtained with the '755A catalyst/cocatalyst system are different from those with a Group VIII metal catalyst in which the metal is weakly ligated to displaceable ligands and a portion of a ligand generates a .sigma.-bond. Whether the .sigma.-bond-generating ligand has an allyl group or a canonical form thereof, the allyl metal linkage provides the initial metal-C .sigma.-bond into which successive NB-type moieties are inserted to form a polymer chain. This insertion reaction is well known in the analogous propagation of ethylene in Ziegler Natta catalysis described in detail in the text Comprehensive Organometallic Chemistry edited by Geoffrey Wilkinson et al, in a chapter titled "Ziegler-Natta Catalysis" by Gavens et al, pg 484 et seq. Allyl-Ni cationic complexes have been synthesized for the polymerization of butadiene, but an allyl-Ni-cyclooctadiene ("allyl-Ni COD") cation complex was reported not to be catalytically active (see text, The Organic Chemistry of Nickel P. W. Jolly and G. Wilke, Vol I Academic Press New York, 1974 pg 352).
On the other hand, it has long been recognized that cationic nickel compounds are active catalysts for the polymerization of butadiene (R. Taube, et al Makromol. Chem., Macromol. Symp. 66, (1993) 245; L. Porri, G. Natta, M. C. Gallazzi, J. of Polymer Sci. Pt C. 16 (1967) 2525). Taube et al state "The chain growth proceeds by the insertion of butadiene into the allyl nickel bond always with formation of the new butenyl group in the `anti` configuration (anti insertion)." The coordination of an allyl type ligand to the nickel is maintained continuously throughout the butadiene polymerization. This mechanism is clearly distinguishable from the insertion mechanism of a NB-type monomer in which insertion of only the very first monomer molecule occurs at an allyl type ligated metal center.
Allylnickelhalides alone (no Lewis acid co-catalyst) have been used to produce polyNB, however the molecular weights of the NB polymer produced in these studies were actually low; e.g. 1000 to 1500 mol wt. (L. Porri, G. Natta, M. C. Gallazzi Chim, Ind (Milan), 46 (1964),428). It had been thought that the low yields and the low mol wts of the polyNB were due to deactivation of the catalysts.
To the best of our knowledge, a norbornyl-Pd cation complex has never been prepared before, for any reason, nor have analogous complexes of Fe, Co, Ru, Rh, Os, Ir or Pt. Such complexes provide a .pi.-bond from an olefin (specifically, from the olefin's double bond), and a .sigma.-bond from a distal C-atom, spaced apart from an olefinic C-atom by at least two single bonds. We recognized that, as used herein, a Group VIII metal cation complex, like a Ni or Pd cation complex, is effective because of the allyl ligand. Both cations initiate and maintain chain growth of a NB-type monomer by the same mechanism, namely one in which the insertion reaction of each successive monomer moiety occurs in the same manner. Neither cation generates a polymer chain of a NB-type monomer in which chain transfer can readily occur, since in each case, the polymer chain generated does not have an available `syn` .beta.-hydrogen for elimination.
Still more recently, in a lone example of the use of a nickel catalyst as a transition metal equivalent to zirconium, Okamoto et al disclosed the production of high mol wt norbornene polymer with a three component catalyst system in example 117 on page 46 of EP 504,418A. The three-component catalyst was made in situ by combining triisobutylaluminum; dimethylanilinium tetrakis(pentafluorophenyl)borate; and, Ni(acac).sub.2 in toluene. The polymer recovered had a M.sub.w =1.21.times.10.sup.6 and a mol wt distribution of 2.37. Though essentially the entire specification is directed to the copolymerization of cycloolefins with .alpha.-olefins using zirconium-containing catalysts, Okamoto et al failed to recognize why they were only able to make a homopolymer of norbornene with a nickel catalyst which, the evidence showed, was different from a zirconium catalyst by its demonstrated distinguishing effect. Though numerous nickel compounds are disclosed in the '418 reference (pg 7, lines 45-52), all but two, allyl(cyclopentadienyl)nickel and bis(cyclooctadiene)nickel, produce no addition polymer in the absence of an alkylaluminum.
The failure to recognize that an .alpha.-olefin might function as a CTA, with or without the presence of an aluminalkyl co-catalyst, was understandable since there existed a large body of work related to the copolymerization of cycloolefins with .alpha.-olefins, and in none of such polymerizations was there any disclosure that the .alpha.-olefin might function as an effective CTA. Further, the great reactivity of ethylene or propylene buttressed an expectation that copolymerization, not chain transfer, is the logical and expected result. That this expectation was unequivocal is evidenced by the reality, that, had a polymerization of a multi-ringed cycloolefin, e.g. NB, been carried out under conditions in which the .alpha.-olefin would have supplied a chain transfer function, the explosive speed of the reaction under normal circumstances would certainly have attracted the attention of the experimenters, as it did ours. To avoid the explosive speed, the polymerization is carried out in a high-boiling solvent present in a large excess, and the reactor is cooled to slow down the reaction.
In particular, the prior art provides no basis to expect the formation of a propagating species by an active insertion-reaction of a NB-type monomer to initiate a "propagating species" generated by a pre-formed, single-component complex in which there is no MAO present. Such a preformed single-component complex may be formed in solution, in situ, and added to one or more monomers; or, the preformed single-component complex may be recovered from solution as a solid, then added to the monomer(s). In either form, whether as solution or as solid, the preformed single-component complex necessarily has a Group VIII metal in combination with a labile bidentate ligand.
Since practical consideration relating to melt-processing cycloolefin addition polymers produced herein, dictate that their mol wt be controlled within one order of magnitude, e.g. in the range from 50,000 to 500,000, it is evident that the '755A invention was unable to provide either a solution to the problem, or even an enabling disclosure to solve it. They do not suggest they can reliably make a reproducible polymer in the defined mol wt range. They suggest the use of hydrogen as CTA, and provided no reason to explore using another, least of all a CTA with a terminal non-styrenic double bond.
Neither is there any basis for estimating the effect of an .alpha.-olefin as a CTA in an insertion reaction, particularly insofar as the .alpha.-olefin is effective to tailor the mol wt of the growing polymer chains in an addition polymerization, irrespective of whether a second component such as MAO is used in a complex catalyst of the type taught by Maezawa.
An acyclic olefin, e.g. 1-hexene, is known to be an effective CTA in the ROMP of cyclic olefins, to reduce mol wt via a cross-metathesis mechanism. ROMP involves a metal carbene (or metal alkylidene) active center which interacts with the cyclic olefin monomer to afford a metallocycloalkane intermediate. A repeating unit contains a C.dbd.C double bond for every C.dbd.C double bond in the monomer. How effectively the acyclic olefin reduces the mol wt of the copolymer formed depends on the structure of the olefin and on the catalyst system (K. J. Ivin, Olefin Metathesis, Academic Press, 1983). In contrast, addition (or vinyl type) polymerization of olefins and diolefins involves the insertion of the monomer into a metal-carbon .sigma.-bond, as in Ni--C, or Pd--C. Despite the many disclosures relating to the formation of copolymers of NB-type monomers, and the well-known fact that an olefin is an effective chain transfer agent in a ROMP polymerization, it will now be evident why the difference in the mechanisms of chain termination failed to suggest the use of an olefin as a chain transfer agent in the copolymerization taught herein.
The critical function of the CTA containing an olefinic bond will be better appreciated in light of the known complexity of phenomena which govern the control of the mol wt of polymers made by transition metal catalyzed polymerization of olefinic substrates to produce saturated addition type polymers.
It is recognized that the known mechanism of ".beta.-hydride elimination" will provide the double bond near the terminal end of the polymer chain. In this mechanism which modulates the mol wt of olefinic polymers, a metal bonded to a hydrocarbyl radical with hydrogens on the carbon .beta. to the metal, can undergo a reaction where the .beta.-hydrogen is abstracted to the metal, leaving an olefinic group. This results in an unsaturated polymer chain and the metal hydride. In general, the rate of .beta.-hydride elimination vs. the polymerization rate, controls the molecular weight of the polymer. For most polymerization catalyst systems, the proclivity of the catalyst system toward .beta.-hydride elimination must be extensively researched and is not predictable. The polymer mol wt depends upon a host of process variables: the choice of monomer or monomers, the ligand environment around the transition metal, the presence of additional donor ligands, type of catalyst (homogeneous or heterogeneous), presence or absence of a co-catalyst (and choice thereof), and polymerization medium (bulk, solution, slurry, gas phase), inter alia.
For example, nickel catalysts have been used in the polymerization of ethylene. Depending upon the Ni catalyst chosen, it is possible to generate exclusively the dimer (1-butene), higher olefins (oligomers), or high mol wt polyethylene. Homogeneous Ni catalysts for the polymerization of ethylene to high mol wt polyethylene have been described by Klabunde et al. (U. Klabunde et al., J. Polym. Sci., Polym. Chem., 25 p 1989 (1987)) and Ostoja Starzewski (P. W. Jolly and G. Wilke, Vol 2, supra) where the polymer mol wt is controlled by the ligand environment around the nickel and the choice of reaction medium. The polymerization of ethylene or propylene has been reported to occur in the presence of a variety of different nickel containing Ziegler catalysts and singlecomponent nickel catalysts, while other nickel catalysts give only dimers (see P. W. Jolly and G. Wilke, Vol 2, supra). Shell Oil Co. uses a nickel-catalyzed oligomerization of ethylene to manufacture linear .alpha.-olefins on a large scale (see G. W. Parshall and S. D. Ittel, Homogeneous Catalysis: The Applications and Chemistry of Catalysis by Soluble Transition Metal Complexes, John Wiley and Sons, 1992).
It is noted that nickel catalysts have been used in the polymerization of butadiene where the solvent is neither a chlorohydrocarbon nor an aromatic solvent such as toluene or xylene. With some catalysts, the microstructure of the polymer is a function of its mol wt. With others, unsaturated hydrocarbons such as acetylenes and allenes retard initiation and propagation and enhance chain transfer, but do not affect microstructure (see Encyclopedia of Polymer Science and Engineering Second Edition, Vol 2; John Wiley and Sons, 1985).
However monoolefins were reported to have no effect on the polymerization of butadiene, at least when the amount added is relatively small (see R. Sakata, J. Hosono, A. Onishi and K. Ueda, Makromol. Chem., 139 (1970) 73). Still other nickel catalysts (with different ligand environments) give only (cyclic) dimers and trimers, such as "COD" and cyclododecatriene ("CDT").
From the foregoing, one would not expect that an olefin would function as an efficient and selective CTA in the addition polymerization of NB-type monomers. It is even more surprising that an olefin is a highly effective CTA in NBE-type polymerizations with catalysts based only on particular Group VIII transition metals.
Most preferably, a polymer in the M.sub.w range from about 50,000 to 250,000 is produced which is readily processable with conventional thermoforming techniques, though tailored polymers with even higher M.sub.w are processable if a monomer is substituted with an alkyl, alkylene or alkylidene substituent. Which substituent is chosen, along with the number of carbon atoms (number of aliphatic carbon atoms) in the chosen substituent, determines the processability and toughness of the polymer.
The polymer produced is preferably thermoformed by extruding it to form articles of arbitrary size and shape, both for optical and non-optical uses. The former use includes molding into lenses, or for example, sheets which are used as components of a flat panel display, or, for multichip modules in which electronic components are sealed. Sheets, tubes and other forms of arbitrary length and cross-section may also be formed by extruding the polymer. Because of the controllable mol wt of the polymer, such forms may be adapted for use as membrane means for the separation of gas from liquid, as in pervaporation membranes; or, in the separation of liquids having different molecular weights as in nanofiltration or reverse osmosis membranes. The polymer produced may also be blended with polyolefins and rubbers to provide toughness and other properties. Such blends are useful to make automobile components such as bumpers, dashboards and for under-the-hood components; and, to make rotors for washing machines, and liners for other appliances such as refrigerators.
If desired, the copolymer of NB-type comonomers may have a high mol wt M.sub.w in the range from 200,000 to 500,000, yet be melt-processable in a desired temperature in the range from 200.degree.-400.degree. C. if a sidechain, specifically, a substituent of known length, is provided on at least one of the monomers. The longer the sidechain, the lower the T.sub.g of the polymer, so that for a melt-processable copolymer with a M.sub.w of about 200,000 only one of the comonomers may have a T.sub.g -lowering substituent; for a M.sub.w of 500,000, preferably each such substituted comonomer has a T.sub.g -lowering substituent. The effect of an alkyl substituent on the T.sub.g of a copolymer was disclosed in an article titled "Synthesis and characterization of poly(5-alkyl-2-norbornene)s by cationic polymerization. Effect of alkyl substituent length on monomer reactivity, polymer structure and thermal properties" by T. Sagane et al, Macromol. Chem. 4, 37-52 (1993). However, the copolymers were made with a AlEtCl.sub.2 /tert-butyl chloride catalyst system, and the mol wt M.sub.w of the longest chain made was less than 2500. There was no suggestion that any other complex metal system, or any other catalyst system might yield higher mol wts.
It should be noted that the structure of the Ni-cyclodiolefin complex has been investigated in the interest of exploring numerous transition metal complexes with weakly ligated compounds in combination with a counteranion. Such a study was published by R. Kempe and J. Sieler in Zeitschrift fur Kristallographie 201, 287-289 (1992) who did not suggest it would have catalytic activity. Also known are compounds related to (.pi.-C.sub.3 H.sub.5 NiCl).sub.2.TiCl.sub.4, which compounds are formed by reacting .pi.-allylnickel halides with strong Lewis acids (e.g. AlBr.sub.3), and these are used for the polymerization of butadiene and the dimerization of olefins. There was no logical reason from known facts about nickel catalysts which would suggest the use of the known metal complex as a particularly effective catalyst for NB-type monomers.